Plant growth-promoting activities of Bacillus subtilis MBI 600 (integral Â^®) and its compatibility with commonly used fungicides in rice sheath blight management

Abstract

Sheath blight (ShB) of rice caused by Rhizoctonia solani is an economically important disease, causing significant yield losses. In this study, the growth promoting activities of commercial formulation of a bioagent, Bacillus subtilis MBI 600 (Integral Â^®) and its compatibility with rice fungicides were evaluated. Integral was evaluated for growth promotion in rice on four cultivars (Cocodrie, Catahoula, Neptune, and Trenasse) under in vitro conditions. Treated rice seeds were incubated for 7 days, and the shoot and root lengths were measured. Rice cv. Cocodrie seeds were treated with strain MBI 600 at various concentrations and seeded in pots containing field soil in GH in a randomized complete block design. Germination and seedling lengths were measured at 7 and 15 days after sowing (DAS). The strain MBI 600 was found to produce siderophores. Seed treatment with Integral significantly increased shoot and root lengths at all concentrations in cvs. Cocodrie, Catahoula, and Trenasse under in vitro conditions. The shoot lengths ranged from 39 to 42 mm at a concentration of 2.20 x 10⁹ cfu/ml in all CV’s. At 2.20 x 10⁹ cfu/ml, the root lengths ranged from 47 to 69 mm. The shoot and root lengths of control seedlings were each up to 20 mm. Seed treatment with 2.20 x 108 and 2.20 x 10⁹ cfu/ml significantly increased seedling emergence (81 to 89%) compared to 2.20 x 10⁶and 2.20 x 10⁷ cfu/ml, and control (61%) under GH conditions. Similarly, seed treatment with 2.20 x 10⁹ cfu/ml of MBI 600 resulted in the highest shoot and root lengths (335 and 166 mm respectively). Integral has good tolerance to hexaconazole, propiconazole, and validamycin; moderate tolerance to tricyclazole; and poor tolerance to benomyl and mancozeb at 1000 ppm. Integral showed compatibility to carbendazim and azoxystrobin up to 400 ppm. Overall, our results suggest that Integral produces siderophores, promoted rice seedling emergence and growth, and is compatible with rice fungicides.